CONSERVATION GENETICS OF BULL TROUT IN THE COLUMBIA AND KLAMATH RIVERDRAINAGES

We used 51 isozyme loci to determine the population genetic structure of bull trout (Salvelinus confluentus) in the Columbia and Klamath Riv er drainages. The sampled populations have little genetic variation wi thin and significant genetic differences among themselves. Preserving the genetic diversity of bull trout will require the continued existen ce of many populations throughout this region Bull trout from the Colu mbia and Klamath drainages would qualify as separate ''species'' under the United States Endangered Species Act according to criteria establ ished for anadromous salmonid fishes. Genotype frequencies at the four variable loci in a group of bull trout used for artificial supplement ation indicate an extremely small number of effective parents. The rel ease of such fish into the wild could have harmful effects on native f ish populations. Non-native brook trout (Salvelinus fontinalis) have b een introduced throughout the range of bull trout, and hybridization b etween these species has been reported Protein and mitochondrial DNA g enotypes collected from one stream in western Montana over an eight-ye ar period indicate the displacement of bull trout by brook trout. This rapid displacement was accompanied by extensive production of intersp ecific first-generation hybrids by both reciprocal crosses.